Detection of micrometastasis in LYMPH nodes using reverse transcription polymerase chain reaction (RT-PCR) for Cytokeratin 20 (CK-20): are we under staging rectal cancer

Abstract

INTRODUCTION: Postoperative adjuvant chemotherapy in rectal cancer is determined by the presence of metastases in lymph nodes. Detection of LYMPH node metastases is routinely performed by light microscopy. Conventional histology may not detect all metastases especially following neoadjuvant therapy (NAT). CK-20 is a cytokeratin known to be specific to colonic epithelium which may help detection of rectal cancer metastases in lymph nodes. OBJECTIVE: To detect micro metastases in lymph nodes in patients with rectal cancer. staged node negative by routine histology. METHODS: Mesenteric lymph nodes from patients who have undergone NAT for rectal cancer were harvested during surgery. Nodes were bisected and one half sent for Haernatoxylin and eosin (H&E) staining and evaluated by a single pathologist, while the other half was examined for CK 20 by RT-PCR. The technique was validated by testing lymph nodes with known metastases and nodes from patients without cancer. 21 lymph nodes from 6 patients (median age 46 years, range 25-55) which were negative for tumour deposits by H&E stain were assessed for micro metastases. RESULTS: All 2 l nodes which were histologically negative for metastases were positive for micro metastases (positive predictive value l 00%) whilst 2 nodes with known metastases were positive for CK-20, 3 nodes from non-cancer patients were negative for CK-20. CONCLUSION: Detection of CK-20 is accurate in identification of micro metastases of rectal cancer to lymph nodes. Assessment of nodes by H&E histology risks under staging lymph node micro metastases in rectal cancer.